The investigators are interested in the mechanism of action and pathologic effects of teratologic antisera. The pathologic events taking place in the rat visceral and parietal yolk sac will be studied with light and electron microscopy in rat embryos exposed to teratogenic antiserum. Antigens from rat kidney and yolk sac which produce teratogenic antiserum will be isolated and will be used to prepare and isolate teratogenic antibodies. Subunits of teratogenic immunoglobulins will be prepared in order to determine whether they maintain their embryopathic effect. The antigenic components of the chorioplacenta will be studied in order to determine which antigens are responsible for the embryotoxic antiserum prepared with term rat placenta. Rabbit anti-ferret yolk sac will be prepared in order to determine whether this antiserum can interfere with ferret development, since the ferret yolk sac is less well developed than in the rats. Studies of yolk sac and chorioplacental function in controls and antibody treated animals will be initiated as well as studies dealing with the biosynthesis of Reichert's membrane as a model of basement membrane synthesis and for the study of the mechanism and significance of the rapidly changing qualities of the parietal yolk sac during rat development. Several tranquilizers which have been recently described to be teratogenic in the mouse and rat will be evaluated with regard to the mechanism of teratogenesis, since preliminary findings in our lab indicate that teratogenesis may be secondary to decreased maternal intake rather than a direct effet of the drug. Finally, the mechanism of implantation failure following uterine vascular clamping will be studied. BIBLIOGRAPHIC REFERANCES: Brent, R.L.: Environmental Factors: Miscellaneous, in The Prevention of Embryonic, Fetal and Perinatal Disease, U.S. Government Publication (1976), in press. Brent, R.L. and Harris, M: The Prevention of Embryonic, Fetal and Perinatal Disease, U.S. Government Publication (1976), in press.